Semiconductor device having a transparent window for passing radiation

ABSTRACT

Method of encapsulating a semiconductor structure comprising providing a semiconductor structure comprising an opto-electric element located in a cavity formed between a substrate and a cap layer, the cap layer being made of a material transparent to light, and having a flat upper surface; forming at least one protrusion on the cap layer; bringing the at least one protrusion of the cap layer in contact with a tool having a flat surface region, and applying a opaque material to the semiconductor structure where it is not in contact with the tool; and removing the tool thereby providing an encapsulated optical semiconductor device having a transparent window integrally formed with the cap layer.

FIELD OF THE INVENTION

The present invention relates to the field of methods of manufacturingsemiconductor devices and to semiconductor devices thus obtained, morein particular to methods of packaging semiconductor devices such as e.g.IR-sensors, in a package having a transparent window for passingradiation, e.g. IR-light, and to devices obtained by such methods.

BACKGROUND OF THE INVENTION

Several packages and packaging techniques for encapsulating integratedcircuits are known in the art, such as glass, metal, ceramic and plasticpackages.

As electronic products increase in functionality and complexity, thereis an emphasis on affordability, miniaturization, and energy efficiencyof the semiconductor devices as a whole. The telecommunications,automotive, and commercial electronic markets are the leading driversfor these trends. These markets see high volume manufacturing withmillions of units on a yearly basis. The choice of the packagingmaterial for the electrical components for these markets can have asubstantial impact on the cost of the final product. Therefore plasticencapsulate components are almost universally used in non-militaryapplications over the conventional ceramic or metal electronic packages.Metal and ceramic packages are mostly used when hermetic packages arerequired, such as in military applications.

Plastic packaging may use organic materials for environmentalprotection. In contrast to hermetically sealed packages, organicmaterial usually contacts the active element (or a thin inorganicbarrier layer) in the plastic package.

Post molded and pre-molded plastic packaging is the dominant technologyin packaging today. Post molded plastic packages are formed after chipsare attached to the mounting surface, such as a metal lead frame, andare electrically connected. Typically, a thermosetting epoxy resin isused to form the package body around the chip and mounting surface.There are many types of post molded packages due to the popularity andversatility of polymers. However, this process does subject the die andwire bonds of the package to the harsh molding environment.

Pre-molded packaging provides a less harsh environment for packagingsensitive chips requiring a low cost assembly. The main element is thatthe chip and interconnects are decoupled from the molding process. Thepackage is made by either a transfer molded process using athermosetting epoxy resin or an injection molding process. The chip andinterconnects are then encapsulated to protect them from theenvironment. In some cases, a plastic lid is used to seal the plasticpackage. The ejection molding process easily produces cavity stylepackages that are increasingly useful for newer optical andelectromechanical chips (MEMS). The injection molding process allows forprecise cavity packages to be manufactured automatically.

EP0813236(A1) describes a method of encapsulating an integratedsemi-conductor circuit, by bringing a column into contact with theintegrated circuit before applying a molding compound, so as to form acavity on top of the integrated circuit when the column is removed. Atube was also used before applying the molding compound so as to createan edge for fixing a window component can be fitted to close the cavity.

US2002/0168795(A1) describes a method for encapsulating a pressuresensor into a package, whereby a mold comprising a pin is used to createan opening in the package. After removal of the pin, an airway iscreated to the pressure sensor.

FIG. 1( a) to FIG. 1( c) are schematic representations of a process thatcan be used for encapsulating an integrated circuit that is sandwichedbetween a substrate (bottom) and a transparent cap layer (top). The moldhas a protrusion which is brought into contact with the cap layer fordefining an opening to be made in the package for allowing passage ofradiation, e.g. light.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide amethod for packaging, in an efficient, easily yet reliable way,semiconductor devices such that the package has a transparent window forpassing radiation.

This objective is accomplished by a method according to embodiments ofthe present invention.

It is also an object of embodiments of the present invention to providea packaged optical semiconductor device with a transparent window.

This objective is accomplished by a packaged optical semiconductordevice according to embodiments of the present invention.

In a first aspect, the present invention provides a method ofmanufacturing a packaged semiconductor device with a transparent window,comprising the steps of: a) providing a semiconductor structurecomprising an opto-electric element located in a cavity formed between asubstrate and a cap layer, the cap layer being made of a materialtransparent to light, and having a substantially flat, e.g. flat uppersurface; b) forming at least one protrusion extending on top of the caplayer; c) bringing the at least one protrusion of the cap layer incontact with a tool having a substantially flat, e.g. flat surfaceregion, and applying an opaque material to the semiconductor structurewhere the latter is not in contact with the tool; d) removing the toolthereby providing a packaged optical semiconductor device having atransparent window.

It is an advantage of this method that it allows a tool with asubstantially flat, e.g. flat surface region to be used, instead of atool having a protrusion for making a cavity. This avoids that adifferent tool needs to be made for each different semiconductor device,but allows the tool to be reused over multiple designs, therebyconsiderably saving on tool costs.

It is an advantage of this method, that it allows for more complicatedshapes to be made, because no tool needs to be extracted from thepackage after the molding material is applied.

It is an advantage of this method that a tool with a substantially flat,e.g. flat surface area can be used, e.g. because such a tool is mucheasier to make and/or clean than a tool with a protrusion as used in theprior art.

It is an advantage of this method that it allows windows of manydifferent geometries to be made, e.g. with a predefined field-of-view,e.g. with a square, rectangular, circular, or an irregular shape.

The solution of the present invention is based on forming a protrusionon or forming part of the cap layer. This is quite different fromforming an opening or through-hole in the enclosure, as was done in someprior art embodiments.

In an embodiment, step (b) comprises removing part of the cap layer.

It is an advantage that the protrusion can be made as part of the caplayer itself.

It is an advantage that the removal of the material of the cap layer canbe performed by standard semiconductor processes, such as lithographicaland etching techniques, which techniques can be extremely accurate.

It is a further advantage that the window is integrally formed with thecap layer, such that the step of connecting a separate window isavoided. In addition, a contact surface between different materials(e.g. between a deposited material and the cap layer) can be avoided,hence also reflections can be avoided.

In a particular embodiment, removing in step b) comprises etching.

Etching is a commonly used technique in the semiconductor industry, thusno special equipment is required.

In an alternative embodiment, step (b) comprises adding a transparentlayer on top of the cap layer.

A preferred method of such adding is depositing of a layer, such as e.g.a Germanium layer. Deposition of the layer has the advantage thatanother material can be used than was used for the cap layer. It is anadvantage that this additional layer may have different properties,which may e.g. be more suitable for particular environments.

Besides deposition, a transparent layer can also be added by way of anyother suitable method, for instance printing.

In an embodiment, step c) comprises inserting the semiconductorstructure in a molding device cavity, and introducing a molding compoundinto the molding device cavity for encapsulating the semiconductorstructure except where the tool is in contact with the protrusion; andwherein step d) further comprises removing the semiconductor structurefrom the molding device cavity.

The molding compound is preferably a plastic material, for instance athermoset plastic material. Possible techniques include transfermolding, injection molding, potting, but other encapsulation techniquesfor encapsulating with e.g. plastic, silicone or other material may alsobe used.

In an embodiment, the method further comprises the step of physically orchemically treating an outer surface of the protrusion.

An example of physical treatment is “polishing”, which may e.g. beapplied for cleaning the surface. Another example may be“sand-blasting”, for increasing its roughness for scattering impinginglight.

It is noted that this step of physical or chemical treatment may beapplied to the protrusion before or after the encapsulation compound isapplied.

In an embodiment, the cap layer in step b) is formed in such a way thatthe resulting protrusion has a first cross-section at a first distancefrom the substrate, and a second cross-section at a second distance fromthe substrate larger than the first distance, whereby the area of thefirst cross-section is larger than the area of the second cross-section.

In an example, the protrusion has a substantially frusto-conical shape,e.g. frusto-conical shape with a larger diameter of a cross-section in aplane closer to the substrate than at its top. Such a shape can e.g. bemade by means of etching, or by means of deposition or printing inseveral steps. Such a shape is impossible to make with prior artmethods, because removal of a tool (e.g. a pin or tube) without damagingthe package necessitates that the tool is cylindrical or tapering to itsdistal end. A frusto-conical shape may be a highly desirable shape whenit comes to optical devices, because it can create sharper images.

In a second aspect, the present invention provides a packaged opticalsemiconductor device having a transparent window, comprising: asubstrate comprising an opto-electric element located in a cavity formedbetween the substrate and a transparent cap layer having a substantiallyflat, e.g. flat upper surface; the cap layer being made of a materialtransparent to light, and having at least one protrusion extending ontop of the substantially flat, e.g. flat upper surface, the protrusionbeing integrally formed with the cap layer; an encapsulating layer madeof an opaque material applied to at least the cap layer and to a sidesurface of the at least one protrusion, a top surface of the protrusionbeing substantially flush, e.g. flush with an outer surface of theencapsulating layer.

It is an advantage that the top of the protrusion is substantiallyflush, e.g. flush with the surrounding area (encapsulated cap layer),which allows easy access to the window, because the window is notlocated at the bottom of an aperture. This enables easy post-treatment,such as e.g. polishing or sand-blasting. In addition, there is no blindhole which can accumulate dust or dirt or moisture, hence the risk ofthe window being obstructed by dust or dirt during actual use of thedevice is reduced, or even eliminated.

In an embodiment, the opaque material is a molding compound.

Preferably thermoset plastic materials are used to encapsulateelectronic devices, but thermoplastic polymer material or siliconematerials could also be used.

In an embodiment, the at least one protrusion has a first cross-sectionat a first distance from the substrate, and a second cross-section at asecond distance from the substrate larger than the first distance,whereby the area of the first cross-section is larger than the area ofthe second cross-section.

An example of such a protrusion forming a window through the package, isa protrusion with a frusto-conical shape.

In an embodiment, the device is an IR-sensor or an IR transmitter.

Particular and preferred aspects of the invention are set out in theaccompanying independent and dependent claims. Features from thedependent claims may be combined with features of the independent claimsand with features of other dependent claims as appropriate and notmerely as explicitly set out in the claims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) to FIG. 1( c) show a method (and mold) that can be used forencapsulating a semiconductor structure while leaving an aperture. FIG.1( a) shows a semiconductor structure and a mold having a protrusionwith a shape corresponding to the aperture to be created. FIG. 1( b)shows the mold in contact with said semiconductor structure, while amold compound is applied. FIG. 1( c) shows the encapsulatedsemiconductor structure after the mold is removed.

FIG. 2( a) to FIG. 2( d) schematically illustrate steps of an example ofa method for manufacturing a packaged semiconductor device, according toan embodiment of the present invention. FIG. 2( a) shows thesemiconductor structure of FIG. 1( a), known in the art. FIG. 2( b)shows the semiconductor structure of FIG. 2( a) after making aprotrusion, and a mold having a flat surface region. FIG. 2( c) showsthe mold in contact with the protrusion, while a molding compound isapplied. FIG. 2( d) shows the packaged semiconductor structure after themold is removed.

FIG. 3 shows steps of a method of manufacturing a packaged semiconductordevice with a transparent window, according to embodiments of thepresent invention.

FIG. 4 shows a first example of a packaged semiconductor deviceaccording to an aspect of the present invention, having one window witha particular field-of-view.

FIG. 5 shows a second example of a semiconductor device according to anembodiment of the present invention, in cross-section, having a conicalwindow tapering at the top.

FIG. 6 shows a third example of a semiconductor device according to anembodiment of the present invention, in cross-section. The devicecomprises a pixel array with two pixels and two windows having adifferent geometry.

In the different drawings, the same reference signs refer to the same oranalogous elements. Any reference signs in the claims, referring to thedrawings, shall not be construed as limiting the scope.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. The dimensions and the relative dimensions do notcorrespond to actual reductions to practice of the invention.

The terms first, second and the like in the description and in theclaims, are used for distinguishing between similar elements and notnecessarily for describing a sequence, either temporally, spatially, inranking or in any other manner. It is to be understood that the terms soused are interchangeable under appropriate circumstances and that theembodiments of the invention described herein are capable of operationin other sequences than described or illustrated herein.

Moreover, the terms top, under and the like in the description and theclaims are used for descriptive purposes and not necessarily fordescribing relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances and that theembodiments of the invention described herein are capable of operationin other orientations than described or illustrated herein.

It is to be noticed that the term “comprising”, used in the claims,should not be interpreted as being restricted to the means listedthereafter; it does not exclude other elements or steps. It is thus tobe interpreted as specifying the presence of the stated features,integers, steps or components as referred to, but does not preclude thepresence or addition of one or more other features, integers, steps orcomponents, or groups thereof. Thus, the scope of the expression “adevice comprising means A and B” should not be limited to devicesconsisting only of components A and B. It means that with respect to thepresent invention, the only relevant components of the device are A andB.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily all referring to the sameembodiment, but may. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner, as would beapparent to one of ordinary skill in the art from this disclosure, inone or more embodiments.

Similarly it should be appreciated that in the description of exemplaryembodiments of the invention, various features of the invention aresometimes grouped together in a single embodiment, figure, ordescription thereof for the purpose of streamlining the disclosure andaiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the detailed description are hereby expressly incorporatedinto this detailed description, with each claim standing on its own as aseparate embodiment of this invention.

Furthermore, while some embodiments described herein include some butnot other features included in other embodiments, combinations offeatures of different embodiments are meant to be within the scope ofthe invention, and form different embodiments, as would be understood bythose in the art. For example, in the following claims, any of theclaimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are setforth. However, it is understood that embodiments of the invention maybe practiced without these specific details. In other instances,well-known methods, structures and techniques have not been shown indetail in order not to obscure an understanding of this description.

With “radiation” in the context of the present invention is meantelectromagnetic radiation of any type which can be detected by adetector element, e.g. light, X-rays, gamma rays. Alternatively, theimpinging radiation may be particles, including low or high energyelectrons, protons, hadrons or other particles.

With “light” in the present invention is meant electromagnetic radiationwith a wavelength between 375 and 1000 nm, e.g. visible light, IR (InfraRed) radiation, near IR or UV (Ultra Violet) radiation, or combinationsthereof.

Where in the present invention a material layer is said to be“transparent” to radiation, e.g. light, what is meant is that theattenuation of radiation passing through said material layer is lessthan a first predefined value, e.g. less than 10 dB, for the predefinedfrequency range (e.g. the frequency range of IR light).

Where in the present invention a material layer is said to be“non-transparent” or “opaque” to radiation, e.g. light, what is meant isthat the attenuation of the radiation passing through said materiallayer is more than a second predefined value, e.g. more than 40 dB for apredefined frequency range (e.g. the frequency range of IR light). If amaterial is opaque to radiation, it can either reflect that radiation,or it can absorb that radiation.

FIG. 1( a) to FIG. 1( c) illustrate a method of encapsulating asemiconductor structure 101. The structure 101 to be encapsulatedcomprises a substrate 104 having semiconductor elements, e.g. aopto-electrical element 102 located in a cavity 103 formed between thesubstrate 104 and a cap layer 105, which cap layer is connected to thesubstrate 104 in a known manner. The cap layer 105 has a substantiallyflat, e.g. flat upper surface 106. Also shown in FIG. 1( a) is a part ofa molding device, e.g. having a molding tool 108 with a protrusion 107.The protrusion 107 of the molding tool 108 has a three-dimensional shapecorresponding to an aperture 111 to be formed in an upper part of theencapsulated device 110 to be made. Thereto the semiconductor structure101 is inserted in a molding device (not shown) and the flat surfaceregion 106 of the cap layer 105 is brought into contact with theprotrusion 107 of the molding tool 108. A opaque molding compound 109 isthen injected in the molding device, for encapsulating the substrate 104and the cap layer 105 at those locations that are not in contact withthe protrusion 107 of the molding tool 108. In particular this meansthat a molding compound of a sufficient thickness, and made of amaterial that is e.g. reflecting or absorbing for the kind of radiationto be measured, e.g. IR radiation, is injected into the molding device.The required layer thickness (d2−d1) (see FIG. 5) depends on thematerial properties of the molding compound. The layer thickness (d2−d1)should e.g. be chosen at least 10 micron thickness for commonly knownand used plastic molding compounds. The molding compound forms a packageof the semiconductor structure with a cavity 111. Hence, the shape ofthe protrusion 107 of the molding tool 108 defines the shape of theaperture 111 of the final device 110. After cooling and removing themold 108, an encapsulated semiconductor device 110 as shown in FIG. 1(c) is obtained. This device has an aperture 111 for allowing radiation,e.g. light, to enter or exit the cavity 111 through the transparent caplayer 6, depending on what kind of opto-electric component or element ispresent in the cavity 103, e.g. an IR-sensor, or a Light Emitting Diode,etc. Of course, the drawings of FIG. 1 are over-simplified, and inpractice the substrate 104 can comprise many other integrated componentsor sub-circuits, such as amplifiers, voltage regulators, processors,etc., and the cap layer 105 may cover only a small part of the substrate104, and the semiconductor structure may be connected to a lead frame,but these aspects are well known in the art, and need not be discussedhere in detail. A problem of this method is that the mold tool 108 needsto be modified for each new semiconductor device, which is costintensive.

Looking for a method which does not require the molding tool 108 to bemodified for each different design, the inventors surprisingly came upwith the idea illustrated in FIG. 2. Instead of providing a tool 108with a protrusion 107 for making an aperture 111, as was done in themethod shown in FIG. 1, a protrusion 7 is made on or in the cap layer 5.This protrusion 7 can be made in several ways, but the preferred way isto etch away part of the upper surface 6 of the cap layer 5 usinglithography, thereby providing a semiconductor structure 1 asillustrated in FIG. 2( b). In this case, the etching step thus definesthe dimensions of the protrusion 7, and thus the amount of FOV (Field OfView) of the window 11. Other ways for making the protrusion are alsoenvisioned, such as e.g. adding the protrusion 7 by way of deposition ofa transparent material, or by printing of a material layer that istransparent for the incoming radiation. An advantage of etching is thatthe process is simple and well known.

This semiconductor structure 1 with protrusion 7 is then inserted in amolding cavity (not shown) and the molding tool 8 with a substantiallyflat, e.g. flat surface region 18 is brought into contact with theprotrusion 7 for preventing molding compound to be applied on the top ofthe protrusion 7. A molding compound 9 is injected in the molding deviceas schematically illustrated in FIG. 2( c). As mentioned above, thelayer thickness and kind of material of the molding compound are chosensuch that the layer is substantially opaque, e.g. opaque for theradiation to be measured. After hardening, and removal from the moldingdevice, an encapsulated semiconductor device 10 as shown in FIG. 2( d)is obtained. As can be seen, the protrusion 7 of the cap layer 5 definesa window 11 in the package where radiation, e.g. light, can enter thecavity 3 from the outside, or can exit the cavity 3 from the insidetowards the outside. The main advantage of this method is that the moldtool 8 does not need to be modified for each new semiconductor structure1 to be packaged, but can be reused over multiple designs, therebysaving considerable tool costs. Another advantage is that the protrusion7 is now made to the cap layer 5, which can be made by standardsemiconductor processes, such as lithographical and etching techniques,which techniques can be extremely accurate, and optionally allows formore complicated shapes than are possible by existing methods. Anotheradvantage is that the mold tool 8 with a substantially flat, e.g. flatsurface area 18 can be cleaned much easier than a mold 108 havingprotrusions 107. Another advantage is that the top of the protrusion 7is substantially flush, e.g. flush with the surrounding area(encapsulated cap layer), which allows easy access to the windowsurface, because the window is not located anymore at the bottom of anaperture (as was the case in FIG. 1( c)). This enables post-treatment,such as e.g. polishing or sand-blasting. In addition, there is no blindhole anymore which can accumulate dust or dirt or moisture, hence therisk of the window being obstructed by dust or dirt is reduced.

Suitable materials for the cap layer 5 include—but are not limitedto—quartz glass, sapphire glass, silicon. A suitable material for beingdeposited on the cap layer 5 for forming the protrusion 7 is e.g. adeposited Germanium layer. The substrate 4 may e.g. be made of sapphire,Si, GaAs, InP, GaP or the like.

The vertical height of the protrusion 7 could be in the range of 10 μmto 300 μm (but the present invention is not limited to this range). Thelateral dimensions of the protrusion 7 could be in the range of 100 μmto 1000 μm (but the present invention is not limited to this range).

FIG. 3 is a flow-diagram showing the steps of a method according toembodiments of the present invention illustrated in FIG. 2( a) to FIG.2( d).

In step 301 a semiconductor structure 1 is provided, comprising a caplayer 5, for example as shown in FIG. 2( a). Semiconductor structures 1comprising a substrate 4 and a cap layer 5 are typically used foroptical semiconductor devices, i.e. comprising integrated circuits withat least one opto-electric component, e.g. an IR sensor. Such structure1 can be made by any suitable semiconductor technique known in the art.

In step 302 a protrusion 7 is formed on the cap layer 5. This may beperformed by removing material from the cap layer 5, e.g. by way ofetching, but other ways to perform the protrusion are also possible,such as e.g. embossing or printing. The shape of the protrusion 7defines the shape of the window 11 to be formed. The result of step 302is shown in FIG. 2( b).

In step 303 a mold tool 8 having a flat surface region is brought intocontact with the protrusion 7 for preventing molding material to bedeposited on top of the protrusion 7. This way, the protrusion 7 willform a transparent channel, also referred to as “window” 11 through theencapsulation or package. Then encapsulation material, e.g. plasticmolding material is applied to the semiconductor structure 1. Thepreferred way of doing so, is to insert the semiconductor structure 1 ina molding device, and to inject a molding compound 9 into the moldingdevice, so as to cover at least the top of the cap layer 5 and the sidesurface of the protrusion 7, and optionally also the side or bottomsurfaces or both of the semiconductor structure 1, as illustrated inFIG. 2( c). The molding compound preferably is opaque for light, so thatlight can only enter or exit to the area underneath the cap layer 5 viathe “window” 11 formed by the protrusion 7.

In step 304 the mold tool 8 is removed, and if the semiconductorstructure 1 was inserted in a molding device, the encapsulatedsemiconductor structure is now removed from the molding device,resulting in the packaged semiconductor device 10 shown in FIG. 2( d),having a window 11 transparent for radiation, e.g. light. In the presentinvention, it is assumed that the device comprises at least oneelectro-optical component or element underneath the cap layer 5, hencethe device 10 of FIG. 2( d) is a packaged optical semiconductor with atransparent window 11, transparent being defined in terms of intendeduse, selected in function of the wavelength of the radiation thepackaged optical semiconductor will be used with.

FIG. 4 shows a three-dimensional top view of an example of asemiconductor device 10 according to embodiments of the presentinvention, having a window 11 with a specific field-of-view (FOV) whichis substantially circular, e.g. circular, but has both an exclusion 15(here: about 1 quadrant, the present invention, however, not beinglimited thereto), and an extension 16 (here: a small rectangle, thepresent invention, however, not being limited thereto). Windows 11having other field-of-views can also be defined.

Whereas the protrusion 7 shown in FIG. 2 is substantially cylindrical,e.g. cylindrical (i.e. have a substantially constant, e.g. constantcross-section in the height direction Z), FIG. 5 shows an example of aprotrusion 7 having a three-dimensional shape which cannot be made bythe method illustrated in FIG. 1, but can be made by a method accordingto embodiments of the present invention. FIG. 5 shows a protrusionhaving a frusto-conical shape tapering to the top (in a direction awayfrom the substrate 4), meaning that a first circular cross-section ofthe protrusion 7 taken at a first distance d1 near the “bottom” of theprotrusion 7 has a larger diameter than a second circular cross-sectionof the protrusion 7 taken at a second distance d2 “near the top”. Thiscould be manufactured e.g. by KOH etching, but the present invention isnot limited to this method. A frusto-conical shape may be particularlyinteresting for obtaining sharp images, as is well known in the art. Butthe present invention is not limited to cylindrical shapes orfrusto-conical shapes, and other three-dimensions shapes can also beused.

FIG. 6 shows a third example of a semiconductor device 10 according toan embodiment of the present invention, in 2D cross-section. This devicehas a pixel array of two pixels, but of course the invention is notlimited thereto, and the array could also have more than two pixels. Inthe embodiment of FIG. 6 each pixel has a window 11, but that is notabsolutely required, and in other embodiments, some pixels may have nowindow. The windows 11 a, 11 b of the different pixels may have the samefeature size, or may have different feature sizes, and they may comprisethe same material (e.g. when made by etching), or different material(e.g. when made by printing). In the specific example shown in FIG. 6,the windows 11 a, 11 b have a circular cross section (in a planeparallel to the substrate), and the diameter of the window 7 a (on theleft of the drawing) is larger than the diameter of the window 7 b (onthe right of the drawing).

In another embodiment (not shown), the semiconductor device has aplurality of windows 11, all having the same geometry.

1. A method of manufacturing a packaged semiconductor device with atransparent window, comprising the steps of: a) providing asemiconductor structure comprising an opto-electric element located in acavity formed between a substrate and a cap layer, the cap layer beingmade of a material transparent to light, and having a substantially flatupper surface; b) forming at least one protrusion extending on top ofthe cap layer; c) bringing the at least one protrusion of the cap layerin contact with a tool having a substantially flat surface region, andapplying a opaque material to the semiconductor structure where thelatter is not in contact with the tool; d) removing the tool therebyproviding a packaged optical semiconductor device having a transparentwindow.
 2. A method according to claim 1, wherein step b) comprisesremoving part of the cap layer.
 3. A method according to claim 2,wherein removing in step b) comprises etching.
 4. A method according toclaim 1, wherein step b) comprises adding a transparent layer on top ofthe cap layer.
 5. A method according to claim 1, wherein step c)comprises inserting the semiconductor structure in a molding devicecavity, and introducing a molding compound into the molding devicecavity for encapsulating the semiconductor structure except where thetool is in contact with the protrusion; and wherein step d) furthercomprises removing the semiconductor structure from the molding devicecavity.
 6. A method according to claim 1, further comprising the step ofphysically or chemically treating an outer surface of the protrusion. 7.A method according to claim 1, wherein the cap layer in step b) isformed in such a way that the resulting protrusion has a firstcross-section at a first distance from the substrate, and a secondcross-section at a second distance from the substrate larger than thefirst distance, whereby the area of the first cross-section is largerthan the area of the second cross-section.
 8. A packaged opticalsemiconductor device having a transparent window, comprising: asubstrate comprising an opto-electric element located in a cavity formedbetween the substrate and a transparent cap layer having a substantiallyflat upper surface; the cap layer being made of a material transparentto light, and having at least one protrusion extending on top of thesubstantially flat upper surface, the protrusion being integrally formedwith the cap layer; an encapsulating layer made of a opaque materialapplied to at least the cap layer and to a side surface of the at leastone protrusion, a top surface of the protrusion being substantiallyflush with an outer surface of the encapsulating layer.
 9. A packagedoptical semiconductor device according to claim 8, wherein the opaquematerial is a molding compound.
 10. A packaged optical semiconductordevice according to claim 8, wherein the at least one protrusion has afirst cross-section at a first distance from the substrate, and a secondcross-section at a second distance from the substrate larger than thefirst distance, whereby the area of the first cross-section is largerthan the area of the second cross-section.
 11. A packaged opticalsemiconductor device according to claim 8, being a device selected fromthe group consisting of an IR-sensor and an IR transmitter.